Four Carriage NER Newcastle, Blyth and Newbiggen set
Paul is building me NER 52ft Brake Thirds to Diagram 76 and 77. The 76 has four compartments (code XB (4)) while the 77 has five (code XB (5)). The company built ninety Diagram 76s and seventy-six Diagram 77s, so they were not a carriage built for niche traffic flows. They were built between 1902 and 1906 for the 76 and 1903 and 1904 for the 77. The 76 being built in 1905/1906 is a bit of a surprise since elliptical roof coaches were already being built.
Here is a shot of a four carriage set allocated to the Newcastle, Blyth and Newbiggen roster number 83. Book-ended by 52ft 5-compartment Diagram 77 Brake Thirds with two 52ft Locker Composites (3 Firsts 4 Thirds) to Diagram 7. the NER had one hundred and thirty-four of those carriages, built between 1896 and 1906 so they had a use for them. Like the Diagram 76, they were still being built when elliptical roof carriages were emerging from the works.
The go-to 52ft Brake Third for the NER after 1895 was the 3 compartment Diagram 18, with one hundred and seventy-six being built up until 1906. It was the usual practise of the company to book-end their carriage sets with Brake Thirds and where 52ft carriages were specified it was mostly a pair of Diagram 18s. This appears to have led to some trains being left with a surfeit of van capacity, which must have meant the company was literally hauling around a lot of empty space. it took its time noticing it, with the first 76s and 77s not appearing until 1902! it would appear that the four compartment type was a "toe-in-the-water" evolution, trading a tolerable amount of van space for a single compartment, increasing the passenger capacity to forty. Once some began work on the company's lines it seems that the traffic managers identified some services where they could trade away even more van space for another compartment, raising the capacity to fifty.
Several years later, in 1907, they decided to try some six-compartment Brake Thirds, though by this time they appeared with elliptical roofs. This seems to have been a step too far for the company, since only one was built in 1907 and a further eight to a different diagram in 1908. Some were produced to the 49ft length for some services and at least one diagram was specifically for excursion work, where presumably van space was a low priority.
What is harder to explain is why pair two five compartment D77s with two locker composites? This means that, in effect a loss of two of the four extra compartments provided by the 5-compartment D77s compared to using 3-compartment D18s.